Inlet screen for an electronic optical image amplifier and method of making it

ABSTRACT

An inlet screen for an electronic optical image amplifier has a luminous layer placed upon a carrier which is followed by a photo cathode. The invention is particularly characterized in that the luminous layer is provided from the center to the edge with an absorbing substance in a manner counteracting the dropping brightness.

United States Patent 1191 Gudden et a1.

[ Aug. 13, 1974 INLET SCREEN FOR AN ELECTRONIC OPTICAL IMAGE AMPLIFIERAND METHOD OF MAKING IT Inventors: Friedrich Gudden, Erlangen;

Wolfgang Schubert, Frauenaurach, both of Germany Assignee: SiemensAktiengesellschaft,

Erlangen, Germany Filed: July 6, 1972 Appl. No.: 269,355

Foreign Application Priority Data July 8, 1971 Germany..' 2134110 US.Cl. ..3 13 101 Int. Cl. HOlj 31/50 Field of Search 313/65 12,65 A, 94,101

[56] References Cited UNITED STATES PATENTS 3,617,791 11/1971 Franz313/94 3,716,713 2/1973 Levin 313/65 R X Primary Examiner-Herman KarlSaalbach Assistant ExaminerSiegfried H. Grimm Attorney, Agent, orFirm-Richards & Geier [5 7] ABSTRACT An inlet screen for an electronicoptical image amplifier has a luminous layer placed upon a carrier whichis followed by a photo cathode. The invention is particularlycharacterized in that the luminous layer is provided from the center tothe edge with an absorbing substance in a manner counteracting thedropping brightness.

3 Claims, 2 Drawing Figures INLET SCREEN FOR AN ELECTRONIC OPTICAL IMAGEAMPLIFIER AND METHOD OF MAKING IT This invention relates to an inletscreen for an electronic optical image amplifier wherein a luminouslayer is placed upon a carrier and is followed by the actual photocathode layer. Such layer arrangements are used in electronic opticalimage amplifiers particularly in order to change X-rays into a radiationwhich has a good effect upon the photo cathode layer. Otherwise X-rayswould have a very little effect upon the'photo cathode layer, since theyare absorbed in the thin layer only to a very small extent.

In known image amplifiers having an inlet screen of the described typethe brightness drops in the outgoing image, namely, parts having thesame brightness appear darker at the edge than in the middle.

An object of the present invention is to improve existing devices ofthis type.

Another object is to balance the described drop in brightness so that auniformly bright image is produced.

Other objects of the present invention will become apparent in thecourse of the following specification.

In the accomplishment of the objectives of the present invention it wasfound possible to provide uniform brightness reproduction in outgoingimages of image amplifiers by providing a layer upon the luminous screenwhich absorbs the light of radiation from the center toward the edgeopposite to the drop in brightness.

In accordance with the present invention this can be accomplished when acarrier of aluminum is used by applying thereon prior to the applicationof the luminous layer an absorbing layer consisting of carbon and thusconstituting a blackening. The application can be carried out bysteaming and can be so regulated by fixed or movable screens that thelayer is thinner in the radial outward direction. This results in thatthe reflection of the carrier increases in the same direction. This alsoprovides an increase in the density of the radiation which istransmitted from the inlet screen edgewise upon the photo cathode. Bysuitable actuation, such as an optical control of the steaming atseveral points, the brightness can be always precisely compensated.

The central coating can be so selected that the total increase of theimage amplifier (Gx) can have any desired value within certain limits(for example, Gx lcd s/m mR, wherein cd =candela, s =seconds, m squaremeters and mR milliroentgens.)

The blackening of the carrier on the side upon which lies the luminousscreen layer results in a substantial improvement in the localtransmission function of the screen. The stronger absorbing coatingwhich increases from the edge toward the center improves the modulationtransmission function in the particularly important center of the imagewithout making worse the'transmission function at the edge at apredetermined radiation density, as compared to a screen having noblackenmg.

lnstead of using the above-described reflection diminishing layer, thedistribution of light can also take place by absorbing substances whichare introduced into the layer or applied thereon in suitable manner.

A feature of the present invention is that the drop in brightness is notcompensated by making the luminous the edge it would be necessary toaccept a noticeable worsening of the transmission function. On the otherhand a thinner coating in the middle would result in an insufficient rayabsorption.

The invention will appear more clearly from the following detaileddescription when taken in connection with the accompanying drawingshowing by way of example only, a preferred embodiment of the inventiveidea.

In the drawing:

FIG. 1 is a diagrammatic partly sectional view through an electronicoptical X-ray image amplifier.

FIG. 2 is a partly sectional view illustrating the making of an inletscreen.

FIG. 1 shows a vacuum tight piston 1 having an inlet screen 3 behind theinlet window 2. The screen is followed, for example, by electrodes 4 and5, an anode 6 and an outlet or viewing screen 7 which can be examinedthrough the end window 8. The inlet screen made in accordance with thepresent invention consists of a carrier calotte 9 carrying in the middlea thicker graphite layer 10 and coated inwardly with a luminous layer 11.

When X-rays pass through the window 2, the carrier 9 and the graphitelayer 10 into the luminous layer 11, light is released therein whichpenetrates into the photo cathode layer 12, which releases theseelectrons; the electrodes 4, 5 and the anode 6 transmit them upon thescreen 7. Due to the acceleration of the electrons and due to thediminution of the image a substantially brighter image is produced inthe screen than could have been expected from the luminosity.

FIG. 2 shows a device for producing the graphite layer 10 extendingtoward the side. The device consists essentially of a vacuum tight jar13 mounted upon an equally tight table 14 and evacuated by a suctionjoint 15. Within the cover 13 there are evaporators l6 and 17 used tocoat the calotte 18. The calotte is mounted as cover upon a cylinder 19which is mounted by rollers 20 and 21 upon the table 14 and which isalso rotated by the motor 22 and the frictional wheel 23, so that thecalotte 18 is uniformly coated even if the centering is not precise.Furthermore shortly before the calotte l8 and within the cylinder 19there is a screen 24 having a free passage in the middle for the strongtreatment of the calotte 18. The coating of the calotte is determined bythe light source 25 and the accordingly set measuring device 26 whichcan be read at an indicating device 28 connected with the device 26 by aline 27.

The unit is operated in that carbon vapor produced in the evaporator 17provides a strong coating in the middle of the calotte 18 while at thesides a shadowing takes place by the screen 24 which is not stronglyrepresented upon the calotte 18, whereby a continuous coating isproduced. The diameter of the opening 29 of the screen is so selectedthat the desired balancing of dropping brightness is produced.

The coating with carbon is terminated when the instrument 28 shows thatpercent of the passing light has been reduced to about 40 percent. Thena luminous substance can be applied by the evaporator 16. However, thescreen 24 must be removed to provide a uniform thickness of the luminouscoating.

When a carrier calotte 9 is used which consists of metal and is nottransparent, the control of the application by transmitted rays cannotbe carried out. However, a mirror (shown by broken lines) can be placedwithin the range of the screen 24 and a testing glass 31 is placed inthe ray passage. A bundle of rays which then passes from the mirror 30to a source 25 directed to the receiver 26, can be collected then in thereceiver 26 which corresponds to the measuring device 26 and can befurther treated in the same manner as in the above-described devices 26to 28.

The vapor application can be also controlled in time. However,reproduction requirements must be met. The data of the vapor applicationmeans are set according to data produced by experience. The control canbe also strengthened by the visual observation of the vapor application.

What is claimed is:

1. In an electronic optical image amplifier, an inlet screen comprisingan outer carrier, a photo cathode layer, a luminous layer extendingbetween said carrier and said photo cathode layer and carried by saidcarrier, and a coating of a light absorbent substance carried by saidluminous layer upon the side thereof directed toward said carrier andbeing the rear side relatively to said photo cathode layer, thethickness of said coating diminishing from the center toward the edgesof said layer to balance the dropping brightness of the layer.

2. A screen in accordance with claim 1, wherein said absorbent substanceis carbon.

3. A screen in accordance with claim 1, wherein the absorbent coatingsets the increase (Gx) of the amplifier according to the formula Gxl00cd s/m mR, wherein cd =candela, s =seconds, m =square meters and mRmilliroentgens.

1. In an electronic optical image amplifier, an inlet screen comprisingan outer carrier, a photo cathode layer, a luminous layer extendingbetween said carrier and said photo cathode layer and carried by saidcarrier, and a coating of a light absorbent substance carried by saidluminous layer upon the side thereof directed toward said carrier andbeing the rear side relatively to said photo cathode layer, thethickness of said coating diminishing from the center toward the edgesof said layer to balance the dropping brightness of the layer.
 2. Ascreen in accordance with claim 1, wherein said absorbent substance iscarbon.
 3. A screen in accordance with claim 1, wherein the absorbentcoating sets the increase (Gx) of the amplifier according to the formulaGx 100cd s/m2 mR, wherein cd candela, s seconds, m2 square meters and mRmilliroentgens.